Relating to automatic injection devices

ABSTRACT

An injection device comprises a syringe extendible against a spring bias from a retracted position in a housing to a projecting injecting position. A spring biased plunger has collapsible elbows which, when the plunger is released, initially engage the end of the syringe to drive it to the projecting position, whereupon arresting of the syringe movement causes the elbows to collapse inside the syringe to allow the plunger to engage and drive the bung.

RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 14/109,363 filed on Dec. 17, 2013, which is a continuation ofU.S. patent application Ser. No. 13/443,384 filed on Apr. 10, 2012,which is a continuation of U.S. patent application Ser. No. 13/072,289filed on Mar. 25, 2011, which is a continuation of U.S. patentapplication Ser. No. 11/630,507 filed Jan. 7, 2008, which is a 35 U.S.C.§371 Application of PCT Patent Application Number PCT/GB2005/002487,filed Jun. 23, 2005, which claims priority to United Kingdom PatentApplication No.: 0414054.7 filed on Jun. 23, 2004. The entire contentsof each of the above applications are herein incorporated by referencein their entirety.

BACKGROUND

There are various forms of automatic injection device which whenoperated cause the needle of a syringe to be moved forwardly so that itprojects from a protective housing prior to actuation of the syringe toexpress a dose of liquid through the needle. It is important to try toensure that the syringe is moved bodily forward to expose the needlebefore the liquid charge is pressurised so that dribbling from theneedle does not occur before the actual injection takes place. It is anobject of this invention to provide a mechanism which operates in thisdesired manner.

SUMMARY

According to the invention there is provided an injection device forcausing a dose of liquid to be ejected from the needle at one end of asyringe located within a housing of the device, the syringe beingmovable by a plunger, upon release of an actuating bias member at oneend of the housing, to move the syringe, from a first position whereinthe needle is shrouded by the housing, to a second position wherein theneedle projects from the other end of the housing, the plunger being inthe form of a rod with a longitudinally centrally located flexibleprojecting portion which, prior to release of said actuating biasmember, is situated beyond the other end of the syringe, such that aprimary movement of the plunger, under the bias of the actuating biasmember, will cause the projecting portion to bear against the other endof the syringe such that the syringe is moved from said first to saidsecond position, whereupon arresting of further movement of the syringe,results in the flexible portion collapsing inwardly so that it entersthe syringe, thus enabling the plunger to move by a secondary movement,within the syringe, into contact with and to act upon a plug to compressthe liquid within the syringe and cause expression of the liquid throughthe syringe needle.

With such an arrangement, the projecting portion will remain in itsprojecting position (in order to move the syringe from the first to thesecond position) until the force increases to such an extent whichallows the projecting portion to collapse inwardly so that the plungercan then move within the syringe to cause the liquid to be expressedthrough the syringe.

The projecting portion can comprise one or more flexible elbowsprojecting beyond the normal circumference of the rod, but compressibleinto said circumference. This could be in the form of two elbows definedeither side of a longitudinal slit in the rod. The elbows could bepre-formed as a pair of arms either side of the longitudinal slitbetween upper and lower solid portions of the rod.

Preferably the injection device will contain a return bias member actingbetween the syringe housing and the other end of the syringe to hold thesyringe retracted within the housing until the actuating bias member isreleased. One or more of the bias members provided within the housingcan be in the form of a coil spring.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be performed in various ways and a preferred examplethereof will now be described, with reference to the accompanyingdiagrammatic drawings, in which:

FIG. 1 is a sectional view through an injection device of this inventionprior to use; and

FIGS. 2 and 3 are similar views showing successive stages of operationof the injection member.

DESCRIPTION

The injection device shown in the drawings comprises a syringe 1 locatedwithin a protective housing 2. The syringe comprises a 3 incorporating aliquid dose held in place by a bung 4 and having a needle 5 throughwhich the dose can be ejected by applying pressure to the bung 4. The 3has an enlarged head 6. A plunger 7 is biased forwardly by a coil spring8, but is held back in a latched position (FIG. 1) until such time as atrigger shown schematically at 11 is actuated to release the plunger andthe spring 8. Prior to use the syringe 1 is held retracted in thehousing 2 by a coil spring 9.

It will be seen that the plunger 7 is in the form of a rod having acentral portion which defines a pair of projecting elbows 10. These canbe pre-formed as part of a moulded plunger 7. The projecting elbowportions 10 are flexible so that they can be moved inwardly to causethat portion of the rod to adopt a circumference similar to that of therest of the rod. As can be seen in FIG. 2, when the plunger is releasedand biased by the spring 8 the expanded region formed by the elbows 10rests against the head 6 of the 3 and the force provided is sufficientto compress the spring 9 until such time as the head 6 abuts the top ofthe housing 2, whereupon further movement of the 3 is arrested. Thecontinual bias created by the spring 8 then causes the elbows 10 to be20 compressed inwardly as they enter into the interior of the 3. Withthe elbows 10 in the collapsed state, the plunger can then moverelatively easily within the 3 so as to act upon the bung 4 and thuscause the contents of the syringe to be ejected through the needle 5.

The illustrated configuration of the plunger 7 provides severaltechnical advantages. It can be moulded integrally. Also the collapsingmovement of the projecting elbows provides an arrangement which canprovide a suitable injection force to cause the needle to enter the skinto a suitable depth, but then provide a relatively low drag against theinner wall of the syringe container so that the major portion of thethrust of the spring for the remainder of its stroke is applied to thebung 4. It will be appreciated that other configurations of collapsingprojection could be used in place of the collapsing elbows.

What is claimed is:
 1. An injection device comprising: a housing; asyringe coupled to a needle at one end and having a syringe barrel withan inner circular circumference, the syringe slideably mounted withinthe housing for movement between a first position relative to thehousing in which the needle is shrouded by the housing and a secondposition relative to the housing in which the needle projects from thehousing; a bung slideably mounted in the syringe and moveable to expel aliquid through the needle; a plunger comprising: an upper solid portionhaving a circular cross-sectional profile, a lower solid portion havinga distal end operable to move a bung and to transmit an expulsion forcethereto, the lower solid portion having a circular cross-sectionalprofile, and a collapsible projecting portion comprising two flexibleelbows on either side of a central void extending along a central axisof the plunger between the upper and lower solid portions, wherein theflexible elbows project outwardly from the central void when theprojecting portion is in a projecting position, and wherein the flexibleelbows are inwardly collapsible toward the central void to fit withinthe inner circular circumference of the syringe barrel when theprojecting portion is in a collapsed position; and an actuating biasmember provided at one end of the housing and operable to move theplunger toward another end of the housing.
 2. The injection device ofclaim 1, wherein the central void is a longitudinally extending slit. 3.The injection device of claim 1, wherein the plunger is integrallymolded.
 4. The injection device of claim 1, wherein movement of theplunger, upon release of the actuating bias member, causes theprojecting portion to bear against an enlarged head of the syringe todrive the syringe within the housing from the first position to thesecond position.
 5. The injection device of claim 4, wherein, when inthe collapsed position, the projecting portion collapses inwardly sothat it enters the syringe, wherein the collapse of the projectingportion enables the plunger to move within the syringe to compress aliquid within the syringe.
 6. The injection device of claim 1, whereinthe flexible elbows are formed by bifurcation of opposite ends of theupper and lower solid portions.
 7. A syringe assembly comprising: asyringe having a distal end couplable to a needle, a proximal end and asyringe barrel having an inner circular circumference; a bung slideablymounted in the syringe; and a plunger comprising: an upper solid portionhaving a circular cross-sectional profile, a lower solid portion havinga distal end insertable into the proximal end of the syringe andoperable to move the bung and to transmit an expulsion force thereto,the lower solid portion having a circular cross-sectional profile and anouter circumference, and a collapsible projecting portion comprising twoflexible elbows on either side of a central void extending along acentral axis of the plunger between the upper and lower solid portions,wherein the flexible elbows project outwardly from the central void in aprojecting position and have an outer circumference greater than theinner circular circumference of the syringe barrel, and wherein theflexible elbows are inwardly collapsible toward the central void to fitwithin the inner circular circumference of the syringe barrel when theprojecting portion is in a collapsed position.
 8. The syringe assemblyof claim 7, wherein the central void is a longitudinally extending slit.9. The syringe assembly of claim 7, wherein the plunger is integrallymolded.
 10. The syringe assembly of claim 7, wherein movement of theplunger, upon release of an actuating bias member in an automaticinjection device, causes the projecting portion to bear against anenlarged head of the syringe to drive the syringe within a housing ofthe automatic injection device from a first position relative to thehousing in which the needle is shrouded by the housing to a secondposition relative to the housing in which the needle is exposed outsidethe housing.
 11. The syringe assembly of claim 10, wherein, when in thecollapsed position, the projecting portion collapses inwardly so that itenters the syringe, wherein the collapse of the projecting portionenables the plunger to move within the syringe to compress a liquidwithin the syringe barrel.
 12. The syringe assembly of claim 7, whereinthe flexible elbows are formed by bifurcation of opposite ends of theupper and lower solid portions.
 13. A syringe plunger, comprising: anupper solid portion having a circular cross-sectional profile; a lowersolid portion having a circular cross-sectional profile and a distal endoperable to move a bung in a syringe barrel and to transmit an expulsionforce thereto; and a collapsible projecting portion comprising twoflexible elbows on either side of a central void extending along acentral axis of the syringe plunger between the upper and lower solidportions, wherein the flexible elbows project outwardly from the centralvoid in a projecting position and have an outer circumference greaterthan an inner circumference of the syringe barrel, wherein the flexibleelbows are inwardly collapsible toward the central void when theprojecting portion is in a collapsed position and the outercircumference of the projecting portion fits within the innercircumference of the syringe barrel.
 14. The syringe plunger of claim13, wherein the flexible elbows are formed by bifurcation of oppositeends of the upper and lower solid portions.
 15. The syringe plunger ofclaim 13, wherein the central void is a longitudinal slit in the syringeplunger.
 16. The syringe plunger of claim 13, wherein the central voidhas an elongated oval cross-sectional profile extending along thecentral axis of the syringe plunger, and wherein the central void has afirst larger width when the projecting portion is in the projectingposition and a second smaller width when the projecting portion is inthe collapsed position.
 17. A syringe assembly, comprising: a housing ofan automatic injection device; a syringe couplable to a needle at adistal end, the syringe slideably mounted within the housing formovement between a shrouded retracted position relative to the housingand an extended injecting position relative to the housing; a bungslideably mounted in the syringe and moveable to expel a liquid dosethrough the needle at the distal end of the syringe; a plunger having anend operable to move the bung and to transmit an expulsion forcethereto; and wherein the plunger is provided with a projecting regionwhich is outside the syringe when the plunger is at a first position butwhich in use, on movement away from the first position, engages aproximal end of the syringe to drive the syringe to the extendedinjecting position, whereupon arresting of further movement of thesyringe causes the projecting region to collapse inwardly so that itenters the syringe to allow the plunger to expel the liquid dose. 18.The syringe assembly of claim 17, wherein the projecting regioncomprises a pair of elbows, wherein an elbow is defined on either sideof a void in the plunger.
 19. The syringe assembly of claim 18, whereinthe pair of elbows is preformed as an arm on either side of the voidbetween spaced front and rear solid portions of the plunger.
 20. Thesyringe assembly of claim 17, wherein the housing is fixed relative tothe syringe.
 21. The syringe assembly of claim 17, wherein theprojecting region of the plunger is configured to drive the syringe inthe automatic injection device from a first position relative to ahousing to a second position relative to the housing such that theneedle projects from the housing.